Former Reno lounge singer Deloris Van Cartier, who once took refuge at St. Katherine's convent in San Francisco to evade a contract hit on her, and in the process, as Sister Mary Clarence, was able to rejuvenate the failing parish by transforming what was the sisters' terrible choir into a successful sacred version of her lounge act, parlays the renown from that experience into a popular Las Vegas show. St. Katherine's Mother Superior, who now along with Sisters Mary Lazarus, Mary Patrick and Mary Robert teach at St. Francis Academy still in San Francisco, ask Deloris to return to perform her magic in teaching the academy's music class, Deloris who accepts in her gratitude for what her now friends, the sisters, did to save her life. Deloris, however, has to reassume her habit-adorned Sister Mary Clarence persona as the academy's by-the-books principal, Father Maurice, and its hard-nosed administrator, Mr. Crisp, would not tolerate a Vegas showgirl among the teaching staff. Deloris finds that the academy, most specifically the music class, is populated by a bunch of kids who have attitude issues in their belief that they are destined to become nothing as no one, in their mind, cares about them. The student with the biggest attitude issue is Rita Watson, that attitude which masks problems at home with her single mother, hairdresser Florence Watson, who quashes what are Rita's true dreams. Deloris also finds that the students view the music class as a proverbial bird course, and will do whatever they can to keep it as a bird course meaning getting rid of 'Sister Mary Clarence' as their teacher. In the process, Deloris discovers that Mr. Crisp, who has a purely economic as opposed to humanistic approach to his job, has recommended that the academy be closed at the end of the school year, and the valuable property sold. If Deloris is able to transform her class into believing in their talents, she, along with what Mary Lazarus, Mary Patrick and Mary Robert discover among the academy's storage, may be part of the school's salvation, that is if they can hide their activities and Mary Clarence's true identity from Crisp.